The invention relates to an arrangement for pre-selecting the cadence of a gas pressure loader of a machine cannon, which is a further development of U.S. Pat. No. 4,273,025 where the same weapon is described in the following words: "Gas-Loading Automatic Weapon I.G.A. Machine Gun". There is already known an arrangement wherein there is branched off via a separate branch the required portion of the propulsion gas which forms during the firing, which is used for driving the gas loader. This portion of the gas is taken out of a nozzle pipe with predetermined cross-section, which nozzle pipe can be exchanged for a nozzle pipe of a different cross-section. For each respective cross-section of the nozzle pipe there corresponds a predetermined cadence range, so that by means of a pre-selected nozzle exchange the transfer from one to the other cadence range is effected. Such an exchange of nozzle pipes is time consuming, and also the machine cannon is not operable or ready to be fired during the time it takes to exchange the nozzles.